Study of Actual State of Wireless Technology in Residential Environments Mo Sha Peng Li Jing Xia

Link study  TelosB  compliant Chipcon CC2420 radio  250 kbps maximum bit rate  Can be programmed to work on 16 channels  Received Signal Strength Indicator (RSSI) to measure signal strength  Spectrum Analyzer  Use Wi-Spy spectrum analyzer  Can track all radio activity from 2.4 GHz  Connected to PC though USB 2 15 Days 5+ GB Data Trace Link Snooping + 2.4GHz Spectrum Scanning

Questions? 1.Is every channel covered by exclusive wireless signal? 2. How long does every channel maintain consecutive clean? 3. Is channel diversify beneficial? 4. Is the interference narrow-band or wide-band? 5. Does the interference change over time? 6. Is there cyclic behavior (time correlation)? 7. Is there correlation between adjacent channels (frequency correlation)? 8. Does the interference mainly cause by Wifi? 9. Is every channel clean if we remove modeled Wifi signal? 10. How many channel become clean if we remove modeled Wifi signal?

Is every channel covered by exclusive wireless signal? RSSI Threshold=30dB+noise floor

Is every channel covered by exclusive wireless signal? RSSI Threshold=40dB+noise floor

Is every channel covered by exclusive wireless signal? Insight: Each channel covered by exclusive wireless signal, but the impact on each channel is different. Impact

How long does every channel maintain consecutive clean? RSSI Threshold=30dB+noise floor

How long does every channel maintain consecutive clean? RSSI Threshold=40dB+noise floor

How long does every channel maintain consecutive clean? Insight: Channel with long-time consecutive clean condition is rare. Impact

Is channel diversify beneficial? Insight: channel diversify is beneficial. With an ideal channel hopping approach

Is the interference narrow-band or wide-band? Insight: The interference is mainly narrow-band, hence channel diversify is helpful.

Does the interference change over time? Insight: The interference on each channel changes over time.

Hamming Distance Purpose Evaluating the difference between two equal length strings Definition Number of positions at which the corresponding symbols are different Normalized Hamming Distance (NHD) Hamming distance divided by the length of string NHD described the difference between two strings Digitalized wireless signals are strings of 0’s and 1’s We use 1-NHD to quantify the similarity (correlation) between two signal sets

Frequency Correlations - 1 Window size = 3 min; Threshold = 30 dBm + Noise floor

Frequency Correlations - 2 Window size = 3 min; Threshold = 40 dBm + Noise floor

Time Correlations - 1 Window size = 3 min; Threshold = 30 dBm + Noise floor

Time Correlations - 2 Window size = 3 min; Threshold = 40 dBm + Noise floor

Signal dependency between channels Window size = 3 min; Threshold = 30 dBm + Noise floor

Signal dependency between channels Window size = 3 min; Threshold = 40 dBm + Noise floor

Wireless Sensors interfered by WiFi  Questions  8. Does the interference mainly cause by Wifi? Days Link Snooping + 2.4GHz Spectrum Scanning

802.11(WiFi channels) and ( TelosB channels)

Does the interference mainly cause by Wifi? Packet Receive Ratio (PRR) TelosB : 16 channels range from 2.405GHz to 2.485GHz PRR of TelosB 16 channels

Percentage of strong signal per second TelosB reciever sensitivity -90dBm (min) -94dBm Threshold = 30dBm + nosie floor Percentage of signal >threshold per second

Correlation of consecutive days of TelosB 16 channels 16 TelosB channels 14 consecutive days 16 TelosB channels 14 consecutive days

Correlation of consecutive days of WiFi 13 channels 14 consecutive days 13 WiFi channels

Conclusion  Random occurrence of WiFi signals (no correlation among time)  High frequency of occurrence of WiFi signals in residential apartments  Interfere with wireless sensors